IntroductionAccording to the American Heart Association (2004), over 79 million Americans have one or more forms of cardiovascular disease (CVD). One in three deaths in the U.S. is attributable to CVD (AHA, 2004). As well, CVD deaths are listed as the top deadliest diseases in the world (See Table 1). The overall objective of cardiac rehabilitation is to restore and maintain physiological, psychological, social, and occupational status in patients with coronary artery disease (CAD) (which is a narrowing of the coronary arteries that supply blood and oxygen to the heart). This intervention also seeks to assist patients with their resumption of daily recreational activities. Traditionally, continuous aerobic activities have been the primary methods of training patients enrolled in cardiac rehabilitation in order to improve and maintain aerobic fitness. High-intensity interval training has been employed and shown to be an effective exercise modality to improve maximal aerobic power in healthy active populations of men and women. Warburton and colleagues note that preliminary data on interval training with some patients with cardiac disease has also led to improved health benefits. Despite the wide-ranging usage of interval training in healthy populations, few studies have evaluated the effect of interval training on the health status of patients with cardiovascular disease. Therefore, the purpose of this study was to examine the underlying benefits of interval training with highly functional patients with CAD.SubjectsThe 14 volunteers in this study were men (ave. age=56 years; ave. weight =190 lbs) who had undergone bypass surgery or an angioplasty (a medical procedure in which a balloon is used to open narrowed or blocked blood vessels of the heart) and were >6 months post-surgery. The subjects were identified in stable condition and highly functional, with peak aerobic capacities >31 m/kg/min, which is about 9 METS. A MET, which equals 3.5 ml/kg/min, is a physiological concept that represents a simple procedure for expressing the energy cost of physical activities as multiples of resting metabolic rate. The researchers grouped the subjects by age, weight and aerobic capacity into one group (n=7) of traditional aerobic training and another group (n=7) of interval training.

Training SessionsBoth training groups were required to train on two days per week of this 16-week study. The traditional aerobic group completed a 10-minute warm-up followed by 30 minutes of continuous aerobic exercise at 65% heart rate reserve (heart rate reserve is the difference between resting heart rate and maximum heart rate), which is also equivalent to 65% of their VO2 reserve. In addition, the subjects performed a standardized resistance training program, which was followed by a 10-minute cool-down. The interval training group performed the same warm-up, resistance training and cool-down segments as the traditional group. However, the interval training groups aerobic workout consisted of 2-minute high-intensity bouts at 90% heart rate reserve followed by 2-minute low-intensity bouts at 40% heart rate reserve, for the 30-minute cardiovascular bout. Both groups training sessions utilized three different types of exercise modes, including combined arm and leg ergometry, treadmill and stair stepping. All subjects were also encouraged to participate in three additional training sessions per week of continuous aerobic exercise at 65% of their heart rate reserve. The researchers confirmed that the volume of the exercise (aerobic and resistance training) performed by both groups in this study was the same.ResultsThe traditional aerobic and interval training groups showed statistically significant and similar improvements in aerobic capacity during this 16-week training study as measured by a maximal treadmill test (subjects were pre- and post-tested using a Bruce maximal stress test protocol, commonly employed in cardiac rehabilitation programs). However, the interval training group showed a significantly greater treadmill time to exhaustion, exercising twice as long as the traditional aerobic group in a specific treadmill test to exhaustion. In this exhaustion test, the subjects exercised at 90% of their heart rate reserve until they voluntarily stopped. This test is valuable for measuring endurance capacity, with the later minutes of the test demonstrating anaerobic capacity markers. Warburton and colleagues explain that as subjects near the end of their aerobic capacity, in the exhaustion test, they will recruit energy from the anaerobic energy systems. Though improvement did occur, no statistically significant changes were observed with either group in systolic and diastolic blood pressure, pulse pressure (which is the difference between systolic and diastolic pressure and a function of stroke volume), artery compliance (extensibility of arteries to facilitate blood flow), or rate-pressure product (which is a measurement of the heart muscles oxygen consumption and is calculated by multiplying the heart rate times the systolic blood pressure).Practical ApplicationWith the pervasiveness of heart disease in all societies throughout the world, fitness professionals and personal trainers should be very familiar with the risk factors to CAD (See Table 2). This investigation demonstrates that functional CAD male patients, with aerobic capacities >31 ml/kg/min, can perform interval training in addition to a continuous cardiovascular exercise program. However, care should always be taken as some patients will posses higher functional abilities than others. Therefore, it is imperative that proper screening, extensive health evaluations, and physician approval be taken to ensure adequate safety precautions during exercise.

Perhaps the most notable finding of this study was the significantly greater time to exhaustion observed in the interval training group. As the authors highlight, it does appear to lead to adaptations that allow for a greater tolerance to a strenuous exercise challenge. These adaptations would be of particular benefit for the performance of many activities of daily living. The bottom line message personal trainers and fitness professionals can share with their physically active and stable CAD clients is that the inclusion of interval training programming will result in them being able to function more efficiently during the day and for lengthier periods of time.

Table 1. The Five Deadliest Diseases in the WorldIschaemic heart disease (reduced blood supply to the heart)
Cerebrovascular disease (damage to blood vessels in the brain, resulting in a stroke)
Lower respiratory infections (pneumonia and influenza are the most common)
HIV/AIDS
Chronic Obstructive Pulmonary Disease (emphysema and chronic bronchitis are most common)
Adapted from: World Health Organization (2004) http://www.who.int/features/qa/18/en/

Table 2. Coronary Artery Disease (CAD) Risk FactorsSedentary Lifestyle Not meeting minimal requirements of 30 minutes of moderate intensity on most days of the week
Cigarette Smoking Current smoker or individual who has quit within 6 months
Hypertension Systolic BP >140 mmHg or Diastolic BP >90 mmHg and verified on two separate occasions
Family History Sudden death before age 55 for father or male 1st degree relative; or before age 65 in mother or other female 1st degree relative
Abnormal Cholesterol TC >200 mg/dl
HDL <40 mg/dl
LDL >130 mg/dl
On lipid-lowering medication
Obesity BMI >30 kg/m2 or waist circumference >102 cm (40 in) for men and >88 cm (35 in) for women
Fasting Blood Glucose >110 mg/dL measured on two separate occasions

BiographiesJonathan N. Mike, MS, CSCS, NSCA-CPT, is a doctoral student in the exercise science program in the Department of Health, Exercise, and Sport Science at the University of New Mexico, Albuquerque (UNM). He earned his undergraduate and graduate degrees in exercise science at Western Kentucky University (Bowling Green, KY) and has research interests in strength and power, exercise metabolism, exercise endocrinology, and neuromuscular physiology.

Len Kravitz, Ph.D., is the Program Coordinator of Exercise Science and Researcher at the University of New Mexico where he recently won the "Outstanding Teacher of the Year" award. Len was honored with the 1999 Canadian Fitness Professional International Presenter of the Year and the 2006 Canadian Fitness Professional Specialty Presenter of the Year awards and chosen as the American Council on Exercise 2006 "Fitness Educator of the Year.